REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



221 



or six to forty), which differ from the zoo- 

 spores, not only in their external form, but in 

 possessing a distinct investing membrane. 

 This complication of structure corresponds 

 with the capability of retaining their vitality 

 for a long period. They may be found in an 

 unaltered condition in the water in which the 

 parent plant has grown for many months 

 after the total destruction of the latter ; and 

 it is to them, doubtless, that we must attri- 

 bute the extraordinary facility with which the 

 Saprolegnia makes its appearance whenever 

 the peculiar conditions it requires present 

 themselves.* On the filaments which produce 

 the above-described spore-cases, there are 

 developed among them, and at the same time 

 with them, slender, worm-like branchlets, 

 These, as they reach the spore-cases, attach 

 themselves firmly to them, and even some- 

 times wind round them in a regular manner. 

 An actual interchange of contents, however, 

 has not yet been observed. f 



2 1 . Reproductive organs of the red Alga; or 

 FloridceE. In this group of plants we unfortu- 

 nately know too little of the origin and deve- 

 lopment of the germ-producing organs, to 

 compare them with the forms which prevail in 

 other groups. It is altogether beyond the 

 limits of the present article to describe in 

 detail all the perplexing varieties of structures 

 to be found in the Florideae which may be 

 supposed to have some relation with the re- 

 productive function. It will be sufficient to 

 mention the three leading forms that are met 

 with, and which may at all times be easily 

 identified, in spite of the innumerable subor- 

 dinate modifications that they undergo. The 

 first form, to which the term polysjmre is 

 usually applied, is that of a gelatinous or 

 membranous pericarp or conceptacle, in which 

 an indefinite number of sporidia are contained. 

 This organ may be placed either at the summit 

 or in the axil of a branch, or it may be con- 

 cealed in or below the cortical layer of the 

 stem. In other cases a number of sporidium- 

 bearing filaments emanate from a kind of 

 placenta at the base of a spheroidal, cellular 

 perisporaiigiiim, by the rupture of which the 

 sporidia which are formed from the endo- 

 chromes of the filaments, make their escape. 

 Other forms, which it does not seem neces- 

 sary to mention, are observed : they all agree 

 in one particular, viz. that the sporidium is 

 developed in the interior of a cell, the wall of 

 which forms its perispore, and the internal 

 protoplasmic membrane (endochrome), the 

 sporidium itself, for the escape of which the 

 perispore ruptures at its apex. 



22. The second form is much more simple, 

 and consists of a globular or ovoidal cell, con- 

 taining in its interior a central granular mass, 



* Pringsheim, I. c. N. A. A. L. C. 1851. p. 417. 



All that is required to obtain a living specimen 

 of this singular plant, is to allow the body of any 

 small animal, such as a fly or spider, to float for a 

 few days in rain water, exposed to the light. By 

 this method a crop of Saprolegnia may be obtained 

 at any season. 



t Braun. /. c. p. 318. 



which, as the organ arrives at maturity, divides 

 into four smaller quadrant-shaped spores, 

 which finally escape by the rupture of the cell- 

 wall. This organ is called a tetraspore; it 

 takes its origin in the cortical layer. The 

 tetraspores are arranged either in an isolated 

 manner along the branches, or in numbers to- 

 gether, surrounded by a whorl of smaller 

 branchlets. In some cases the form of the 

 branches which contain tetraspores is so com- 

 pletely modified by their presence, that they 

 assume the appearance of special organs, 

 which are called stichldia, as, for example, in 

 Dasya.* 



23. It is with respect to the third kind of 

 reproductive ovgan, the antheridium, that the 

 greatest differences of opinion exist; all observ- 

 ers, however, agreeing as to the general sig- 

 nification to be attached to it. The antheridia 

 are always produced on different individuals, 

 but in precisely the same situations as the 

 tetraspores and polyspores. They are " ag- 

 glomerations of little colourless cells either 

 united in a bunch, as in Griffithsia, or enclosed 

 in a transparent cylinder, as in Polysiphonia, 

 or covering a kind of expanded disc of 

 peculiar form, as in Laurencia." -j- According 

 to the researches of Derbes and Nageli , 

 each of these cellules contains a spermatozoid. 

 Nageli describes it as a spiral fibre, which, as 

 it escapes, lengthens itself in the form of a 

 screw. Derbes, on the other hand, describes 

 it as "a hyaline globule, furnished with a 

 flagelliform appendage, by means of which it 

 agitates itself with a very active motion, which 

 lasts for some moments." According to M. 

 Thuret, who certainly is to be considered a 

 higher authority than either of the above men- 

 tioned, each cell of the antheridium is occupied 

 by a hyaline corpuscle, spherical in Polysi- 

 phonia, ovoidal in other genera. These cor- 

 puscles, however, whose contents are granular, 

 offer no trace of a spiral filament, but are ex- 

 pelled from the cells by a slow motion, which 

 Thuret compares to that observed in the ex- 

 pulsion of the tetraspores from their theca. 

 The antheridia appear in their most simple 

 form in Calithamnion, being reduced to a mass 

 of cells, composed of numerous little bunches, 

 which are sessile on the bifurcations of the 

 terminal branches. The woodcut represents 

 the antheridium of Griffithsia, in w hich species, 

 it is produced like the tetraspores, in a sort 

 of lateral involucre of verticillate branchlets. 

 Each of these bifurcates, and bears at the 

 bifurcation a pyramidal antheridium, which 



* See H. H. Harvey, Nereis Boreali Americana, 

 Part ii. passim. New York, 1852. The best 

 descriptions of the organography of the Florideaj 

 will be found in the Essay of Decaisne on the Clas- 

 sification of the Algre in the Ann. des Sc. Nat. 1842 ; 

 and in Nageli's Zeitschrift, f. w. Bot. Heft. 3 & 4. 

 Zurich, 1846. 



f Thuret, Ann. dcs Sciences Nat. o mc Ser. xvi. 



J Derbes, Ann. des Sciences Nat. 3 me Ser. xiv. 

 2G1. ; These de Botanique, p. 25. Paris, 1848. 



8 Nageli, /. c H. 3 & 4. S. 224. Zwei Bemer- 

 kungen, &c. Bot. Zeit. 1850. 32 Stuck. 



